JPS63236517A - Dehumidification method for mixed gas - Google Patents

Abstract

PURPOSE:To remove selectively water vapor effectively from various kinds of mixed gas at a high removal rate by using an aromatic polyimide gas separating membrane and carrying out gas separation at a specific temperature or more. CONSTITUTION:Mixed gas containing water vapor is continuously fed from a mixed gas feed opening 3 at a temperature of 60 deg.C or more into a gas separation device 1 with a built-in aromatic polyimide gas separating membrane 2, and the mixed gas is flowed along the gas feeding side of the gas separating membrane 2. The water vapor in the mixed gas permeates the gas separating membrane 2 efficiently by carrying out gas separation of the gas separating membrane 2 at the temperature of 60 deg.C or more, and the mixed gas (impermeable gas) sufficiently dehumidified and dried is prepared on the gas feeding side of the gas separating membrane 2, and said gas is exhausted out of an impermeating gas exhaust outlet 4. The water vapor permeating the gas separating membrane 2 is exhausted and removed out of a permeating gas exhaust outlet 5.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a gas separation membrane (hollow fiber,
Various mixed gases containing water vapor (e.g.,
The present invention relates to a method for selectively removing water vapor from air, nitrogen, argon, natural gas, accompanying gas during crude oil extraction, fermentation gas, etc.) and drying a mixed gas.

[Conventional technology and its problems]

Conventionally, as methods for dehumidifying hydrocarbon gases such as natural gas, glycol absorption methods, molecular sheep adsorption methods, and the like have generally been employed.

However, all of these methods require fairly large equipment, have high equipment costs, and require sufficient land for factory construction, making them difficult to use in offshore gas extraction where space is limited. is not suitable, and also the complexity of the operation,
There were also problems in terms of operational safety and difficulty in maintenance.

In contrast to the above-mentioned absorption and adsorption methods, gas separation equipment with a built-in gas separation membrane has recently been developed as a method that can be made smaller and lighter, is easier to maintain, and is highly safe. Several methods have been proposed for dehumidifying or drying mixed gas.

As a method for dehumidifying a mixed gas using such a gas-containing Wn film, for example, the following method is known.

+8+ Pressurize the mixed gas containing water vapor to an extremely high pressure and supply it to the gas separation device, or significantly reduce the pressure on the permeate side of the gas separation membrane, so that the supply side and the permeate side of the gas separation membrane are separated. A method of dehumidifying a mixed gas by increasing the differential pressure of water vapor (see JP-A-54-152679).

(bl) The permeability of the main component of the supply gas (for example, methane gas in natural gas) is relatively high, and the selective permeability of water vapor to methane gas (P II□0/PC114
) is 200 to 400, a method of dehumidifying a mixed gas (see Japanese Patent Laid-Open No. 59-1!113835).

+c+ A method of dehumidifying a mixed gas by supplying a large amount of purge gas to the permeation side of a gas separation membrane to lower the partial pressure of the water vapor (see JP-A-50-2674).

(d) A method of dehumidifying a mixed gas by using a gas separation membrane made of aromatic polyimide having a specific water vapor permselectivity and flowing dry gas through the permeation side of the gas separation membrane (JP-A-62 (Refer to Publication No.-42723).

However, in the above-mentioned known method (al is the area where the concentration of water vapor is high on the gas permeation side of the gas separation membrane (
(near the permeated gas outlet), it may not be possible to remove water from the mixed gas at a sufficiently high removal rate, and this is not suitable for practical use.

Further, the above-mentioned known method (BL) has a problem in that it is difficult to manufacture a gas separation membrane having gas separation performance suitable for this method.

Further, the above-mentioned known method (C1) has the problem of consuming a considerably large amount of purge gas.

Further, the above-mentioned known method fdl is the above-mentioned known method fdl.
al~(C1), but there were problems such as insufficient removal of water vapor and the need to introduce dry gas to the permeation side of the gas separation membrane.

[Means for solving problems]

As a result of intensive research to provide a practical dehumidification method that solves the problems in the method J for dehumidifying a mixed gas using a gas separation membrane, the inventors of the present invention have developed a gas separation membrane made of aromatic polyimide. When a gas separation device with a built-in membrane (hollow fiber membrane, spiral membrane, flat membrane) was operated and operated at a specific temperature, dehumidification or drying of the mixed gas was performed using conventional methods. It has been found that this process can be carried out effectively with a sufficiently high removal rate compared to the conventional method.

The present invention has been made based on the above findings.In a method for dehumidifying a mixed gas containing water vapor using a gas separation device incorporating a gas separation membrane, an aromatic polyimide film is used as the gas separation membrane. The present invention also provides a method for dehumidifying a mixed gas, characterized in that gas separation in the gas separation membrane is performed at a temperature of 60° C. or higher.

Hereinafter, the mixed gas dehumidification method of the present invention will be described in detail with reference to the drawings.

The aromatic polyimide gas separation membrane used in the present invention is
The selective permeability (gas separation performance) indicated by the "ratio of gas permeation rates of water vapor and nitrogen (P) 1.0/PNz)" measured by the gas permeation test method described below is preferably 50 or more, more preferably is 200 or more, more preferably 5
It is a gas separation membrane made of aromatic polyimide and has a molecular weight of about 00 to 5ooo. The above selective permselectivity (P HzO/P Nt
) is less than 50, which is not appropriate because the loss of the mixed gas increases.

Further, the gas separation membrane has a permeation rate C of water trace air at 25°C.
PlhOi (according to the gas permeation test method described below) is about I
10-'cd/c+a-sec-cmHg or more,
Especially l x l Q-' ~5 x 10-"cd/c
It is preferable that it is about d·sec -cnHg.

The gas separation membrane is preferably an aggregate of hollow fibers with a large effective membrane area, but may also be a spiral membrane, a flat membrane, or the like.

The outer diameter of the hollow fiber used as a gas separation membrane is usually 50 to 2000μ, preferably 200 to 1000μ. If the outer diameter of the hollow fiber is too small, pressure loss will increase, and if it is too large, the effective membrane area will decrease. Further, as the hollow fiber, it is preferable to use one that satisfies the condition of (thickness/outer diameter) -0.1 to 0.3, and the above-mentioned thickness - (
Outer diameter - inner diameter/2. If the thickness of the hollow fiber is small, the pressure resistance may be insufficient, and if the thickness is large, the water vapor selective permeability may be poor.

The above-mentioned aromatic polyimide gas separation membrane contains an acid component such as aromatic tetracarboxylic acid or its acid dianhydride,
Aromatic polyamic acid (or aromatic polyimide) obtained by polymerizing (and imidizing) an aromatic diamine component
A gas separation membrane with an asymmetric structure (a membrane that has a homogeneous layer and a porous layer integrated) formed by a wet membrane forming method using a coagulating liquid, or an aromatic polyimide solution, etc. It is a composite separation membrane manufactured by forming a thin homogeneous layer on the surface of a porous membrane made of a suitable material, and has sufficient gas separation performance for water vapor as described above.

The above-mentioned aromatic polyimide particularly contains 20 to 100 mol%, preferably 40 to 100 mol%, of an aromatic diamine containing a -8-1 or -502- divalent group j. A material obtained by polymerizing and imidizing an aromatic diamine component and an aromatic tetracarboxylic acid component in approximately equimolar amounts is extremely suitable in terms of high water vapor transmission rate.

Examples of the aromatic diamine containing the divalent group j of "-8-1 or -3O□-" include diamino-dibenzothiophene or its derivatives, diamino-diphenylene sulfone or its derivatives, diamino Diphenyl sulfide or its derivatives, diamino-diphenyl sulfone or its derivatives, diamino-thioxanthin or its derivatives, etc. can be mentioned.

In particular, the diamino-dibenzothiophenes or derivatives thereof include diamino-dibenzothiophenes represented by the general formula, and examples of the diamino-diphenylene sulfone or derivatives thereof include diamino-dibenzothiophenes represented by the general formula. Diphenylene sulfones may be mentioned. However, the above general formulas (1) and (II)
In, R and R' are hydrogen, a hydrocarbon substituent having 1 to 6 carbon atoms (alkyl group, alkylene group, aryl group, etc.), an alkoxy group having 1 to 6 carbon atoms, etc., such as a methyl group. , ethyl group, propyl group, etc. are suitable.

The diamino-dibenzothiophenes represented by the above general formula (1) include 3,7-diami2-2,8-dimethyl-dibenzothiophene, 3,7-diami2,2,6-
Dimethyl-dibenzothiophene, 2,8-diamino-3
, 7-dimethyl-dibenduthiophene, 3,7-diami-2,8-diethyl-dibenzothiophene, and the diamino-diphenylene sulfones represented by the above general formula (II). is 3°7-
diami2, 8-dimethyl-diphenylene sulfone,
3.7-diamino-2,8-diethyl-diphenylene sulfone, 3,7-diamino-2゜8-dipropyl-diphenylene sulfone, 2,8-diamino-3,fucymethyl-diphenylene sulfone, 3.7-diamino-3, fucymethyl-diphenylene sulfone 2.8
-dimethoxy-diphenylene sulfone and the like.

Furthermore, the above diamino-diphenyl sulfide or its derivatives include 4,4'-diamino-diphenyl sulfone, 3,3'-diamino-diphenyl sulfone, 3'-diamino-diphenyl sulfone, 3.
．． Diamino-diphenyl sulfones such as 5-diamino-diphenyl sulfone, 3.4'-diamino-diphenyl sulfone, and 4.4'-diamino-diphenyl sulfide, 3.3'-diamino-diphenyl sulfide, 3.5- Diamino-diphenyl sulfide, 3゜4
Diamino- such as '-diamino-diphenyl sulfide
Diphenylsulfides can be mentioned, and the above-mentioned diamino-thioxanthin or its derivatives include 3,7-cyamino-thioxanthin-5,5-dioxide, 2,8-diamino-thioxanthin-5,5-dioxide, 3゜7-siamitsu-thioxanthone-5.5-
Dioxyto, 2,8-diamino-thioxanthone-5°5-dioxide, 3,7-cyamitsu-phenoxatine-5,5-dioxide, 2,8-diamino-phenoxatine-5,5-dioxide, 2,7-cyamitsuthian Threne, 2,8-diamino-thianthrene, 3,7-cyamitsuIO-methyl-phenothiazine-5,5-dioxide, and the like can be mentioned.

Further, as the aromatic diamine, bis((p-
aminophenoxy)phenyl] sulfide, bis[(p
-aminophenoxy)phenyl]sulfone.

As the aromatic diamine component used in the production of the aromatic polyimide, other aromatic diamines are used together with the aromatic diamine containing the above-mentioned "r3-1 or 15oz-divalent group". and such other aromatic diamines include 4,4°-diamino-diphenyl ether, 3,3°-dimethyl-4,4°-diamino-
Diphenyl ether, 3,3°-jetoxy-4°4'
Diphenyl ether compounds such as -diamino-diphenyl ether and 3.3゜-diamino-diphenyl ether, diphenylmethane compounds such as 4,4゛-diamino-diphenylmethane and 3,3゛-diamino-diphenylmethane, 4゜4゛-diamino-benzophenone ,3,
Benzophenone compounds such as 3'-diamino-benzophenone, 2,2-bis(3-aminophenyl)propane, 2,2-bis(4-aminophenyl)propane, 2
, 2,2-bis(phenyl)propane-based compounds such as 2-bis(4-(4°-aminophenoxy)phenyl)propane, and further 0-2m-19-phenylenediamine,
Examples include 3,5-diaminobenzoic acid, 2,6-cyamitsupyridine, and 0-tolidine.

Further, the aromatic tetracarboxylic acid component used in the production of the aromatic polyimide is 3°3', 4.4
'-biphenyltetracarboxylic acid, or 2.3.3'
, 4'-biphenyltetracarboxylic acid, dianhydrides thereof, or lower alcohol esters thereof, etc. Category 1, 3,
3°, 4.4'-benzophenonetetracarboxylic acid,
Or 2,3.3'.

Benzophenonetetracarboxylic acids such as 4°-benzophenonetetracarboxylic acid, dianhydrides thereof, or lower alcohol esters thereof;
Examples include pyromellitic acid MI\I such as pyromellitic acid, its dianhydride, or its esterified product.

In particular, in the present invention, biphenyltetracarbon a[-5
0 to IQ O-1: JL/%, especially 80 to 100-t
The aromatic polyimide obtained from the aromatic tetracarboxylic acid component and the aromatic diamine component described above has excellent solubility in organic solvents such as phenolic compounds. Therefore, it is preferable from the viewpoint of film forming, such as preparation of a stable dope for film forming and film forming properties.

The aromatic polyimide gas separation membrane used in the present invention is
An organic solvent solution such as aromatic polyamic acid (polyimide precursor) obtained from the above-mentioned aromatic diamine component and aromatic tetracarboxylic acid component, or an organic solvent solution of aromatic polyimide, is used as a dope liquid for film formation. A dry method is used to form a thin film of the dope solution, and the film is formed mainly by a drying process in which the solvent is removed from the thin film of the dope solution and solidified, or a thin film of the dope solution is brought into contact with a coagulation solution. A wet film forming method is used to form a membrane by coagulation, and it can be formed into a flat membrane or hollow fiber shape to produce polyimide separation membranes of various structures.

For example, the method for manufacturing the aromatic polyimide gas separation membrane used in the present invention involves using an aromatic diamine component consisting of the above-mentioned aromatic diamine (which may contain other aromatic diamines) and the above-mentioned biphenyl diamine. An aromatic tetracarboxylic acid component mainly containing tetracarboxylic acids is polymerized and imidized in one step in approximately equimolar amounts of a phenolic compound in an organic solvent at a temperature of about 140°C or higher to produce an aromatic polyimide. and a solution of the aromatic polyimide (concentration: about 3 to 30% by weight)
) is used as a dope liquid and applied or cast onto a substrate at a temperature of about 30 to 150°C or extruded into a hollow fiber shape,
A thin film (flat film or hollow fiber) of the dope liquid is formed, then the thin film is immersed in a coagulation liquid to form a coagulation film, the solvent, coagulation liquid, etc. are evaporated and removed from the coagulation film, and finally 150 An example of the Ha manufacturing method is to form an asymmetric gas separation membrane made of aromatic polyimide by sufficiently drying and heat-treating at a temperature of ~400°C, especially 170~350°C.

The gas separation device used in the present invention incorporates the above-mentioned aromatic polyimide gas separation membrane, and examples of such a gas separation device include, for example, a hollow fiber-shaped gas separation membrane as shown in FIG. An example is a gas separation device 1 in which a gas non-separation membrane (which may be a spiral membrane, a flat membrane, etc.) 2 made of aromatic polyimide is housed in a sealed container 6.

The sealed container 6 communicates with the gas permeation side of the gas separation membrane 2 and the gas supply side of the gas separation membrane 2 with an outlet 5 for the permeated gas (water vapor, etc.) that has passed through the gas separation membrane. "Raw material gas supply port (mixed gas supply port) 31,
Any sealed container (for example, a cylindrical container) having a non-permeable gas outlet 41 may be used.

The gas separation membrane (a bundle of hollow fibers, etc.) 2 has a disk shape at both ends formed by solidifying a suitable thermosetting resin such as an elastomer resin, an acrylate resin, an epoxy resin, or a phenolic resin. The resin walls 7, 7° are bound together to form a gas separation membrane element, and
In this element, each hollow fiber penetrates the inside of the resin wall at least at one end (i!!exhaust gas outlet 5 side), and the hole inside the hollow fiber opens toward the outside of the resin wall. As shown in FIG. 1, the resin walls 7, 7' are hermetically fixed to the inner wall of the sealed container 6 using an adhesive or the like if necessary.

In order to carry out the method of the present invention, for example, the above-mentioned gas separation apparatus 1 having a built-in aromatic polyimide gas separation membrane 2 as shown in FIG. Gas is continuously supplied from the mixed gas supply port 3 at a temperature of 60°C or higher, preferably 70°C or higher, more preferably 80 to 150°C, and the mixed gas flows along the gas supply side of the gas separation membrane 2. By doing so, the gas separation operation and operation in the gas separation apparatus 1 may be performed at a temperature of 60°C or higher. By performing the gas separation in the gas separation III2 at a temperature of 60°C or higher in this way, the water vapor in the mixed gas efficiently permeates the gas separation membrane 2, and the gas supply side of the gas separation membrane 2 is sufficiently dehumidified and dried. A mixed gas (non-permeable gas) is obtained.

The dehumidified and dried mixed gas is discharged from the non-permeable gas discharge port 4.

Furthermore, water vapor and the like that have permeated the gas separation membrane 2 are discharged and removed from the permeated gas outlet 5.

In the present invention, the removal of water vapor to the gas permeation side of the gas separation membrane 2 can be adjusted by the temperature of the mixed gas supplied to the gas separation membrane 2 of the gas separation device 1.

The mixed gas to be treated in the method of the present invention mentioned above includes gases such as air, nitrogen, and argon, hydrocarbon gases,
In a mixed gas whose main components are natural gas, petroleum gas, etc.
Examples include those containing water vapor.

Note that when supplying the mixed gas to the gas supply side of the gas separation membrane 2, the gas permeation side of the gas separation membrane 2 may be maintained at a reduced pressure.

In addition, in the present invention, when the pressure at the time of exhausting the permeated gas (water vapor) is near atmospheric pressure, it is necessary to set the pressure at about 2 kg/cj or more, particularly about 5 to 10 g/cd, to remove water vapor. preferred in order to increase the rate.

[Effect]

In the present invention, gas separation operations and operations in a gas separation device incorporating an aromatic polyimide gas separation membrane are carried out at 60°C.
The reason why the water vapor in the mixed gas can be efficiently removed by carrying out the process at the above temperature is presumed to be due to the following reason.

The aromatic polyimide gas separation membrane (hollow fiber 11l) used in the present invention has a water vapor permeation rate from room temperature to 120°C.
On the other hand, the permeation rate of various mixed gases containing water vapor (e.g., air, natural gas, etc.) increases as the temperature increases. Furthermore, the mixed gas supplied to the gas separation membrane has a dilute content of easily permeable components such as water vapor, and the gas separation membrane has a high permselectivity < p
ut.

/PN, is 500 or more at room temperature), the water vapor concentration on the gas permeation side of the gas separation membrane becomes high and the partial pressure difference becomes small, resulting in a small apparent water vapor permeation rate and a decrease in the efficiency of the effective membrane surface. descend. Therefore, when the temperature of the gas separation operation and operation in the gas separation device is set to a range of 60° C. or higher, the permeation rate of the main component (for example, nitrogen, etc.) of the mixed gas becomes several to several times faster than the value at room temperature. On the other hand, since the water vapor permeation rate is almost constant without being affected by temperature as described above, the water vapor concentration on the gas permeation side of the gas separation membrane is diluted to about 1/2 to 115. Therefore, the partial pressure difference increases and the efficiency of dehumidification improves.

〔Example〕

EXAMPLES Hereinafter, the present invention will be explained in more detail by giving examples of the present invention together with comparative examples.

In the present invention, the gas permeation test is carried out using a gas separation device as shown in Fig. 1, which is equipped with a gas separation JIl (hollow fiber) made of aromatic polyimide to separate a mixed gas containing water vapor from approximately At the same time, the inside of the hollow fiber was heated to about 30 Torr while supplying the gas to the gas separation device at a supply pressure of 7 g/cd G and a predetermined measurement temperature (60 to 120 °C in the following example).
Gas separation was performed while evacuation under reduced pressure, and the composition of the gas that did not permeate through the gas separation membrane and the amount of each component that did not permeate (water vapor was analyzed using a DuPont Model 303 hygrometer, and the amount that did not permeate was determined using a soap film i-pointer). ) was measured.

Example 1 Six hollow fibers made of the following aromatic polyimide (effective membrane area: 1
2.0 cd) is sealed with epoxy resin at both ends, and is connected to the raw gas supply port of the gas separation device using a gas separation device built in a sealed container of the same type as shown in Figure 1. , a mixed gas containing 0.281 mo1% water vapor and mainly nitrogen was heated to 7°0 at a pressure of g/cA G,
The gas was supplied at a temperature of 60° C. and a gas flow rate of 120 cnl/sec to flow along the outer surface (gas supply side) of the hollow fiber membrane, while the inner surface (gas permeation side) of the hollow fiber membrane was
The pressure was evacuated to 0 Torr. The non-permeable gas (dehumidified gas) that did not pass through the hollow fiber membrane was collected from the non-permeable gas outlet of the gas separation device, and its composition and flow rate were measured. The results are shown in Table 1 below.

[Aromatic polyimide hollow fiber]

1 o of biphenyltetracarboxylic acid dihydrate.

parts by weight, 80 parts by weight of diamino-dimethyl-diphenylene sulfone isomer mixture, and 20111 parts of 2,6-riamitubiridine, outer diameter: 530μ, inner diameter: 382μ, measurement temperature. Oki thin air permeation rate i 1.8 x 10-' at 25°C
(c+4/cd-sec ・c+sHg).

Examples 2 and 3 Water and gas were removed from the mixed gas in the same manner as in Example 1, except that the raw material gas supply temperature was 80° C. or 120° C. The results are shown in Table 1 below. 1 Comparative Example 1 Water vapor from the mixed gas was removed in the same manner as in Example 1, except that the raw material gas was supplied at 45°C. The results are shown in Table 1 below.

Table 1 [Effects of the Invention] The method of the present invention performs gas separation operation and operation at a temperature of 60°C or higher using a gas separation membrane made of aromatic polyimide, and has the following advantages. ing.

la) Enabling the gas separation membrane built into the gas separation device ξ
can be used for “integrated into the entire gas separation device”
- Since the membrane area of the gas separation membrane used can be reduced, it is possible to downsize the gas separation device.

(b) It is also possible to use a relatively low-pressure raw material gas, and the mixed gas can be dehumidified even if the differential pressure between the raw material gas supply side and the gas permeation side of the gas separation membrane is not very large. be able to.

(c++ The dry gas (non-permeable gas) after the humid operation has been sufficiently dehumidified.

(The water vapor content of the d+ non-passing gas can be controlled over a wide range without changing the raw material concentration, feed rate, membrane area, operating pressure, etc.).

te1 The aromatic polyimide gas separation membrane used in the method of the present invention has extremely excellent properties such as durability, heat resistance, chemical resistance, and moisture resistance, so it can stably dehumidify mixed gas over a long period of time. can be implemented.

[Brief explanation of the drawing]

Figure 1 shows the amount of aromatic polyimide gas used in the method of the present invention +1! FIG. 1 is a cross-sectional view showing an example of a gas separation device incorporating a membrane. ■... Gas separation device, 2... Aromatic polyimide gas separation membrane (hollow fiber), 3... Raw material gas supply port (mixed gas supply port), 4... Non-permeable gas discharge port, 5... Permeation Gas outlet, 6... Sealed container, 7... Resin wall

Claims (1)

[Claims] A method for dehumidifying a mixed gas containing water vapor using a gas separation device incorporating a gas separation membrane, wherein an aromatic polyimide membrane is used as the gas separation membrane, and the gas separation in the gas separation membrane is performed at 60°C or higher. A mixed gas dehumidification method characterized in that the dehumidification is carried out at a temperature of .